1. Technical Field
The present invention relates to a method for efficiently and stably producing a polycarbonate excellent in the transparency, hue, heat resistance, thermal stability, light resistance and mechanical strength and less contaminated with an extraneous matter.
2. Background Art
A polycarbonate is generally produced using bisphenols as a monomer ingredient and by making use of its superiority such as transparency, heat resistance and mechanical strength, is widely utilized as a so-called engineering plastic in the fields of electric•electronic parts, automotive parts, optical recording mediums, optics such as lens, and the like.
The conventional polycarbonate is produced using a raw material derived from petroleum resources, but in recent years, depletion of petroleum resources is feared, and it is demanded to provide a polycarbonate using a raw material obtained from biomass resources such as plant.
In addition, because of a concern that global warming due to increase or accumulation of carbon dioxide emissions may bring about climate change or the like, development of a polycarbonate using, as a raw material, a plant-derived monomer that is carbon neutral even when discarded after use is demanded.
Under these circumstances, a method for obtaining a polycarbonate by using, as a monomer ingredient, isosorbide (ISB) that is a dihydroxy compound obtained from biomass resources, and allowing transesterification with a carbonic acid diester to proceed while distilling of a byproduct monohydroxy compound under reduced pressure, has been proposed (see, for example, Patent Documents 1 to 6). The polycarbonate obtained from ISB has excellent optical characteristics and is known to be usefully usable as an optical material.
However, a dihydroxy compound such as isosorbide exhibits low thermal stability as compared with bisphenols and has a problem that coloration of a resin occurs due to thermal decomposition during a polycondensation reaction performed at a high temperature.
In order to solve such a problem, there have been proposed a method where the surface area of a reaction solution is gained by using a horizontal stirring reactor to raise the reaction efficiency and a polymerization reaction is thereby performed with less heat history (see, Patent Document 7).